This is a U.S. national stage of application No. PCT/DE96/00489, filed on Mar. 15, 1996. Priority is claimed from that application and from the following applications: German Application No.: 195 12 945.8, Filed: Mar. 28, 1995.
The invention is directed to a catalytic pipe for an endothermic catalyst reaction of a process medium.
Endothermic catalytic reactions are generally carried out in reaction spaces constructed in the shape of elongated tubes or pipes which are filled with a bulk particulate catalyst. The process medium to be processed by the endothermic reaction is introduced at one end of the catalytic pipe and discharged at the other end. In order to maintain the reaction, the pipe jacket or pipe casing is acted upon by a heating medium so that an indirect transfer of heat can take place in relation to the process medium. A reactor constructed in this manner has the disadvantage that the heat contained in the product formed by the catalytic reaction is discharged from the reactor space along with this product. This results in a correspondingly high energy consumption.
In order to reduce energy consumption, it is known to form the catalytic pipes as regenerative catalytic pipes. A corresponding reactor is described in EP 0 369 556 B. A basic illustration of this catalytic pipe is shown in the form of a longitudinal section and a cross section in FIGS. 6 and 7. The catalytic pipe has an elongated (e.g., 3 to 14 m length) outer cladding tube 1 which can be heated externally, e.g., by hot flue gases. The two end sides of the cladding tube 1 are tightly closed by bases 2 and 3, wherein the upper base 2 is constructed as a removable flange cover which allows the particulate catalyst to be introduced. In the interior of the cladding tube 1, a rising pipe 6 is arranged coaxial to the longitudinal axis of the cladding tube 1, extends substantially along the entire length of the cladding tube 1, and terminates the lower part near to the base 3 so as to leave open a through-gap. In the upper part, the rising pipe 6 is guided laterally through the casing of the cladding tube 1. A feed line 9 for the process medium to be supplied is arranged just below the base 2. The product formed by the catalytic reaction can be discharged below the base 2 through the outlet 4. The annular intermediate space between the inner surface of the cladding tube 1 and the outer surface of the rising pipe 6 is filled with a bulk particulate catalyst 5. When the process medium is directed downward over the catalyst 5 via the feed line 9 and the cladding tube 1 is heated externally, an indirect heat transfer exchange takes place from the heating medium to the process medium, so that the process medium is heated to the reaction temperature and the endothermic reaction is maintained by the transfer of heat. The endothermic catalytic reaction is concluded as soon as the medium to be processed has left the catalytic bath and arrived in the region of the lower base 3. The direction of flow of the medium reverses in this region and the formed product is directed upward through the rising pipe 6 and discharged through the outlet 4. The product flowing past the inner wall of the rising pipe 6 can give off heat to the process medium through the wall of the rising pipe 6. In this way, at least a considerable portion of the heat contained in the product can be recovered and used to carry out the endothermic reaction. In order to intensify the indirect heat exchange between the product and the process medium, a heat transfer promoter which is constructed as a flow displacement body 8 is arranged coaxially in the interior of the rising pipe 6. In the shown example, this heat transfer promoter is designed as a tubular hollow body and is tightly closed at its upper end face so that the product cannot flow through the interior of the flow displacement body 8. Instead, the flow is compelled to flow through the annular gap 7 between the rising pipe 6 and the flow displacement body 8. The flow velocity of the product is accordingly noticeably increased and the heat exchange rate is increased. However, while this solution is advantageous with respect to heat exchanger technique, the volume occupied by the flow displacement body 8 cannot be used.
A reactor which is outfitted with catalytic pipes that are constructed in a similar manner to regenerative catalytic pipes is known from GB 22 01 903. However, instead of an individual rising pipe, a rising pipe arrangement comprising two rising pipes is arranged in the interior of the cladding tube. The rising pipes run partially parallel to one another and partially in the shape of a helical line in the longitudinal direction. Accordingly, the ratio of the outer surface of the rising pipe arrangement to the flow cross section for the product gas is greater than with an individual rising pipe having the same flow cross section. Accordingly, the heat exchange between the product gas and the process gas guided through the catalyst bed is improved.
An object of the invention is to provide a catalyst pipe having improved heat transfer characteristics and which exhibits an efficient use of the pipe volume for the catalyst bed.
The above stated object is obtained by a catalyst pipe of the invention.
In the invention, a catalyst pipe is formed of an outer cladding tube which is tightly sealed at its end sides by a first base and a second base. One of the bases can be opened to introduce a catalyst into the tube. The tube is externally heatable by a heating medium. A feed line for supplying the process medium to the catalyst filling is also provided.
A rising pipe arrangement of at least one line strand is arranged in the interior of the cladding tube and is preferably substantially coaxially arranged with the cladding tube. The rising pipe arrangement terminates in a collector which is connected in the vicinity of the base with an outwardly directed outlet for the product formed by the catalysis of the process medium. The rising pipe arrangement terminates shortly before the second base of the cladding tube so as to leave a through-gap. A catalyst filling is arranged in the intermediate space between the cladding tube and rising pipe arrangement.
The line strand can be formed of a plurality of separate pipes and a plurality of line strands can be combined to form a physical unit. Optionally, the pipe sections can be flattened or corrugated and welded together. The one or more line strands can be arranged in an approximate star-shaped cross section. Preferably the surface ratio of the cladding tube outer surface to the outer surface of the rising pipe arrangement is less and 3.0 and the cladding tube cross section area is reduced by less than 20%.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects obtained by its use, reference should be made to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.